1. Technical Field
The present invention relates detection of moving objects within a defined space using microwave radiation.
2. Background Art
Systems for detection of the presence of humans and animals in a defined area or space are well-known and are commonly used, for example as intrusion detection systems. With regard to vehicles, for example, it is common today to use intrusion detectors in order to provide an alarm in the event that the presence of a human or an animal is detected within the passenger compartment of the vehicle. In this manner, it can be expected that the risk for theft of the vehicle can be decreased.
A system for presence detection in a vehicle may comprise a combined radio transmitter and receiver based on microwave technology, which means that the radio transmitter is arranged for emitting microwave radiation into a specified space corresponding to the vehicle's passenger compartment. Furthermore, the receiver is arranged for detecting any microwave radiation which is reflected as a result of humans or animals being present in said space. In order to achieve this, it is previously known to use microwave-based detection units of the so-called Doppler motion sensor type. Such units are based on the Doppler shift phenomenon in order to detect motion of humans and animals in a space.
Patent document U.S. Pat. No. 6,426,716, which is herein incorporated by reference, teaches a motion sensor based on a microwave transceiver apparatus. The apparatus comprises a transmit pulse generator being arranged to control the length of the transmit pulses, and thereby, in part, the range of the transceiver.
In the field of intrusion detection, especially in vehicle intrusion detectors, it may be preferable that intrusion only be detected in a very well-defined space, i.e. corresponding to within a well-defined distance from the detector. In such case, the components used in the system, in particular the microwave transmitter and receiver, must be very accurate and of high quality so that the detection sphere can be defined in an exact manner within the vehicle. Otherwise, there will be a risk for false alarms if for example a person or animal passes just outside of the detection sphere. Consequently, there is a need for improved systems arranged for precisely regulating the detection boundaries around an intrusion detector—which means that false alarms can be minimized or preferably eliminated—while still using components and circuit solutions at a relatively low cost.